Magnetic head for perpendicular recording and magnetic disk storage apparatus mounting the head

ABSTRACT

A magnetic head is composed to diminish disordered writing bits of a recording layer or reading noise caused by a magnetic field generated from an under layer without decreasing a writing magnetic field strength of the magnetic head. The magnetic head includes a write head provided with a main pole and one or more auxiliary poles, a read head provided with a read element, and coils located on both sides of the main pole in a manner to sandwich the main pole. The coil located on one side generates the asymmetrical magneto-motive force for magnetizing the main pole to that generated by the coil located on the other side.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present Invention relates to a magnetic head for perpendicularrecording and a magnetic disk storage apparatus provided with the headmounted thereon.

2. Description of the Related Art

In general, the magnetic disk storage apparatus is composed so that datamay be read or written on a recording medium by using a magnetic head.In order to increase a recording density per a unit area of a magneticdisk, it is necessary to decrease a size of recording bit. In thelongitudinal magnetic recording system, however, a smaller recording bitdisadvantageously causes a recording written magnetization on a mediumto be lost by thermal fluctuation. This disadvantage brings aboutdifficulty in enhancing the recording density. As the effectivetechnique in overcoming this difficulty, the perpendicular recordingsystem may be referred which is composed to record (or write) themagnetization in the perpendicular direction to the medium.

The perpendicular recording system may be roughly divided into onesystem composed to have a double layered perpendicular medium consistingof a recording layer served as a recording medium and a soft under layerand the other system composed to have a single layered perpendicularmedium having no under layer. The system composed to use the doublelayered perpendicular medium as a recording medium needs the so-calledsingle pole type head provided with a main pole and an auxiliary polefor writing data.

The provision of the soft under layer leads to increasing a writingmagnetic field strength obtained by the write head but also leadsdisadvantageously to giving rise to a failure caused by the under layeritself. For example, magnetization on the under layer is changedaccording to the recorded bits on the recording layer and the write headfield. This change brings about a magnetic field, which may disturb thewriting bits written on the recording layer or be observed as noise whenreading the magnetizing signal with a read element. Moreover, a certainkind of distribution of the change of magnetization may bring about alarge magnetic field from the under layer.

A magnetic head having a plurality of auxiliary poles and coils has beenknown, an exemplary one of which is described in the following patentpublication 1 and non-patent publication 1. The techniques disclosed inthese publications are prepared for a stray field and do not make anyallowance for the ratio of the magneto-motive force of a coil. Further,if the head is structured to have only one auxiliary pole, the coils arelocated symmetrically. This structure disables to suppress the noisecaused by the change of magnetization of the under layer.

Patent Publication 1 . . . . Official Gazette of Japanese PatentLaid-open No. 2001-250204 Non-patent Publication 1 . . . Pages 163 to168 of IEEE Transactions on Magnetics. Vol. 38, No. 1, 2002

SUMMARY OF THE INVENTION

The magnetic field caused by the change of magnetization of the underlayer, which may disadvantageously disturb the magnetization signalwritten on a recording layer or be observed as noise when reading themagnetization signal with the read element, leads to a great obstacle inrealizing high-density recording.

It is therefore an object of the present invention to provide to reducethe noise caused by the change of magnetization of the under layerwithout decreasing the writing magnetic field strength of a write head.

The inventors of the present invention found out the following fact. Asa result of analyzing the magnetic fluxes of the single pole type headand the under layer, it is possible to diminish the magnetic fluxflowing through the under layer without greatly lowering the writingmagnetic field strength as well as to suppress the disturbance of therecorded bits and the reading noise, both of which are brought about bythe under layer, if the coils are located on both sides of the mail poleasymmetrically, concretely, the product of a number of windings and acurrent applied to the coil located on one side of the main pole isdifferent from that of the coil located on the other side thereof.

According to an aspect of the invention, the magnetic head includes awrite head having a main pole and one or more auxiliary poles and a readhead having a read element and looped thin-film conductor coils locatedon both sides of the main pole in a manner to sandwich the main pole,the magneto-motive force (product of the number of windings and anapplied current) of one coil being different from that of the othercoil.

The use of the single pole type head having the coils structured tocause the magneto-motive forces asymmetrically makes it possible toprovide the magnetic head for perpendicular recording that brings aboutno disturbance of the recorded bits and no reading noise resulting fromthe under layer. The mount of this type of single pole type head mayprovide a magnetic disk storage apparatus having a more improvedrecording density than the conventional apparatus.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph useful of explaining the effect of a magnetic headaccording to the present invention, in which a magnetic flux density ofan under layer is being diminished;

FIG. 2 is a sectional model view showing a structure of a single poletype head according to a first embodiment of the present invention;

FIG. 3 is a conceptual schematic view showing a magnetic disk storageapparatus, for better understanding of the present invention;

FIG. 4 is a schematic view showing relation between a magnetic head forperpendicular recording and a magnetic disk, for better understanding ofthe present invention;

FIG. 5 is a schematic view useful of better understanding perpendicularrecording;

FIGS. 6A, 6B are views illustrating reduction of a magnetic flux densityof the under layer included in the first embodiment of the presentinvention;

FIGS. 7A, 7B are views illustrating reduction of a magnetic flux densityof the under layer included in the second embodiment of the presentinvention;

FIG. 8 is a model view showing the second embodiment of the presentinvention and a structure of a write and read composite head having asingle pole type head according to the present invention;

FIG. 9 is a model view showing a third embodiment of the presentinvention and a write and read composite head having a single pole typehead according to the present invention; and

FIG. 10 is a model view showing a fourth embodiment of the presentinvention and a structure of a write and read composite head having asingle pole type head according to the present invention.

DESCRIPTION OF EMBODIMENTS

Hereafter, the present invention will be described with reference to theappended drawings.

At first, for better understanding of the invention, the schematiccomposition of a magnetic disk storage apparatus will be described. FIG.3 is a schematic view showing the magnetic disk storage apparatus (inwhich view the magnification factors are not unified). The magnetic diskstorage apparatus is composed so that a magnetic head 14 is floated on amagnetic disk 11 being in rotation when writing or reading themagnetization signal. The magnetic head 14 is mounted on a slider 13fixed at the tip of a suspension arm 12 and is positioned by a rotaryactuator 15.

FIG. 4 is a schematic view showing relation between a magnetic head forperpendicular recording 14 and the magnetic disk 11 (in which view themagnification factors are not unified, the head section is illustrated,and the main components are simplified). As is obvious from this figure,the magnetic head 14 is composed of a read head 16 and a write head 18.The read head 18 is composed of two shield films located vertically in amanner to sandwich a read element 8. The write head 14 is composed of amain pole, an auxiliary pole and a looped thin-film conductor coillocated between these poles and served as magnetizing the main pole. Theupper shield layer located on the side of the write head may beintegrally formed with and served as the auxiliary pole of the writehead.

FIG. 5 is a conceptual view showing perpendicular recording (in whichview the head section is illustrated and the main components aresimplified). A magnetic circuit is formed so that a magnetic fieldgenerated from the main pole 1 passes through an under layer 20 andenters the auxiliary pole 3. By applying target current to a coil 2, itis possible to apply a magnetic field in a predetermined direction fromthe main pole 1 onto a recording layer 19 and then record a targetmagnetization pattern on the recording layer 19. As a magnetic diskmedium may be formed an intermediate layer between the recording layer19 and the under layer 20. The read element 7 may be a giantmagneto-resistance effect element (GMR) or a tunnel magnetic-resistanceeffect element (TMR). In FIG. 5, a numeral 17 denotes a rotatingdirection of the disk. The auxiliary pole 3 is located on the leadingside 25 of the main pole 1.

First Embodiment

FIG. 2 is a sectional model view showing the first embodiment of asingle pole type write head used in the present invention. In thisembodiment, the write head is composed of a main pole 1, an auxiliarypole 3 and thin-film conductor coils 2 a and 2 b located on both sidesof the main pole 1 in a manner to sandwich the main pole 1. Theschematic model view of FIG. 2 sectionally illustrates the magnetic headin the disk rotating direction from the center of the disk track, inwhich view the magnification factors are not unified. The two coils 2 aand 2 b may be composed so as to be connected in the disk rotatingdirection so that a magnetic field of the same polarity may be generatedat the tip of the main pole 1. Or, these coils 2 a and 2 b may becomposed to separate these coils 2 a and 2 b from each other so thateach coil generates the magnetic field of the same polarity at the tipthereof.

As is obvious from FIG. 2, in this embodiment, the number of windings ofthe coil 2 a located on the side where the auxiliary pole is notprovided is more than that of the coil 2 b located between the main poleand the auxiliary pole so that the magneto-motive force of the coil 2 bis greater than that of the coil 2 a. In addition, the auxiliary pole 3may be formed integrally with and served as the upper shield of the readhead.

FIGS. 6A, 6B show the magnetic flux density distributions of the underlayer in which the two coils have respective magneto-motive forces, forcomparing the head of the conventional structure (FIG. 6A) with thesingle pole type head of the present invention (FIG. 6B). In FIGS. 6Aand 6B, the tones specified by the scales indicate the correspondingmagnetic flux densities, in which more dense portions correspond withhigher magnetic flux densities. Further, in FIGS. 6A and 6B, themagnetic flux density distribution shown in the right hand concerns withonly the portion enclosed by the dotted line of the schematic model viewof the magnetic head as viewed from the floating surface shown in theleft hand.

In the magnetic flux density distribution shown in FIG. 6A or 6B, thereal line indicates an auxiliary pole 3, while the main pole 1 isrepresented by a dot because it is too small in the scale of thesefigures. Hence, the form of the main pole 1 cannot be visible. Herein,it is assumed that the under layer 20 is composed of a material having asaturation magnetic flux density of 1.2 T. The head of the conventionalstructure (coil: 0.30 AT) shown in FIG. 6A is composed so that themagnetic flux density of the under layer reaches 1.13 T as a maximumvalue. On the other hand, in the head structure of the presentinvention, the magnetic flux density formed in the under layer reached0.59 T as a maximum value because the coils 2 a and 2 b locatedasymmetrically on both sides of the main pole 1 have the magneto-motiveforces of 0.10 AT and 0.20, respectively. In these cases, theconventional structure has a writing magnetic field strength of9.0×10⁵[A/m], while the head structure of this embodiment has a strengthof 8.5×10⁵[A/m]. That is, the reduction was less than 10%. It wasrevealed by the tones of FIG. 6B that the head structure of thisembodiment has a smaller maximum value of the magnetic flux density aswell as a smaller whole magnetic flux density of the under layer 20.This resulted in reducing the noise caused by the under layer 20.

In FIGS. 6A to 6B, the magnitude of the magnetic flux density isrepresented by variable tone and also is divided into the areas 1 to 15.

FIG. 1 is a graph that is useful of explaining the effect of themagnetic head of this embodiment. Concretely, the graph of FIG. 1 showsthe changes of maximum value of the magnetic flux density of the underlayer 20 and the write head field strength against the ratio of themagneto-motive forces of the two coils 2 a and 2 b located on both sidesof the main pole 1. The axis of ordinate represents the normalizedmagnetic flux density of the conventional structure. As is obvious fromFIG. 1, by changing the ratio of the magneto-motive forces of the twocoils 2 a and 2 b, it is possible to reduce the magnetic flux density ofthe under layer 20. For example, by making the magneto-motive force ofthe coil 2 b located on the side having no auxiliary pole 1.5 timelarger than the coil 2 a located between the main pole 2 and theauxiliary pole 3, it is possible to reduce the magnetic flux density ofthis embodiment into 60% of that of the conventional structure. Further,in this embodiment, it is preferable to keep the ratio of themagneto-motive forces of the two coils 2 a and 2 b (coil 2 b/coil 2 a)2.5 or less. If the ratio of magneto-motive force (coil 2 b/coil 2 a) is2.5 or less, the magnetic flux density of the under layer 20 may bereduced into 60% of the conventional structure as keeping the reductionof the writing magnetic field strength 10%.

Further, this embodiment is composed so that the coils 2 a and 2 b haverespective number of windings, that is, are located asymmetrically onboth sides of the main pole. In place, it may be composed so that thecurrent values to be applied to the coils 2 a and 2 b may be changed askeeping the number of windings of each coil constant. This compositionmakes it possible to obtain the coil structure in which the coilsgenerate their respective asymmetric magneto-motive forces. Moreover, bymaking the current values to be applied to the coils 2 a and 2 b and thenumbers of windings of the coils different from each other, the coilsmay generate the asymmetric magneto-motive forces.

The auxiliary pole 3 may be located on the trailing side of the mainpole 1 or the leading side thereof. The auxiliary pole may be providedon one side or both sides of the main pole so that both sides of themain pole may have respective densities of the magnetic fluxes flownfrom the main pole to the auxiliary pole.

Further, the coils may be located on both sides of the main pole in thetrack width direction.

Second Embodiment

FIGS. 7A, 7B show the magnetic head according to the second embodimentof the invention. The views of these figures show the magnetic fluxdensity distribution in the case that the distance D1 between the mainpole 1 and the auxiliary pole 3 (that is, the distance between theopposed side of the main pole 1 to the auxiliary pole 3 and the opposedside of the auxiliary pole 3 to the main pole) is changed into 3 μm, forcomparing the head of the conventional structure (see FIG. 7A) with thesingle pole type head of the present invention (see FIG. 7B). In theconventional structure shown in FIG. 7A, by narrowing the distance D1more than the distance D1 of 15 μm, the distribution of a greatermagnetic flux density is made wider. On the other hand, in the headstructure of the invention shown in FIG. 7B, even if the distance D1between the main pole 1 and the auxiliary pole 3 is made narrower, themagnetic flux density of the under layer 20 is made smaller.

In FIGS. 7A and 7B, the magnitude of the magnetic flux density isrepresented by variable tones and also is divided into the areas 1 to15.

Hence, as shown schematically in FIG. 8 (schematic section of the trackcenter in the disk rotating direction), the head structure of theinvention allows the distance D1 between the main pole and the auxiliarypole (between the opposed side of the main pole 1 to the auxiliary pole3 and the opposed side of the auxiliary pole 3 to the main pole) to benarrowed to a film thickness T1 of the coil 2 a and a film thickness T2of an insulating layer (served as insulatively separating the coil 2 afrom the main pole 1 and the auxiliary pole 3) without having toincrease the magnetic flux density of the under layer 20. That is, thedistance between the main pole and the auxiliary pole may be madesmaller to [number of coil layers×T1+(number of coil layers+1)×T2]. Thethickness T2 of the insulating layer may be made smaller to 100 nm inconsideration of its pressure resistance. This makes it possible tonarrow a distance D3 between the read element 7 sandwiched between alower shield 8 and an upper shield 9 to the opposed side of the mainpole 1 to the read element. Thus, as shown in FIG. 8, this embodimentmay offer a read and write composite head that is suitable to thehigh-density recording. In addition, in FIG. 8, the auxiliary pole 3 maybe integrally formed with and served as the upper shield 9.

Third Embodiment

FIG. 9 is a schematic sectional view showing a magnetic head accordingto a third embodiment of the present invention, in which view the readelement 7 and the auxiliary pole 3 are located in a manner to sandwichthe main pole 1 and the coils are located on both sides of the main polein an asymmetrical manner, that is, in a manner to apply respectivemagneto-motive forces onto both sides of the main pole as described withrespect to the foregoing first and second embodiments. The section iscut on the center of the track in the disk rotating direction.

In this embodiment, no auxiliary pole 3 is provided between the readelement 7 and the main pole 1, so that the distance D3 between the readelement 7 and the opposed side of the main pole 1 to the read element 7may be made narrower by the film thickness. Moreover, since the magneticflux being flown from the main pole 1 to the upper shield 9 issuppressed, it is preferable to make the distance D2 between the uppershield 9 and the main pole 1 (in particular, the distance between theopposed side of the upper shield 9 to the main pole and the opposed sideof the main pole 1 to the upper shield) greater than the distance D1between the opposed side of the main pole to the auxiliary pole and theopposed side of the auxiliary pole to the main pole.

Further, in order to suppress the magnetic flux being flown into theupper shield 9, in this embodiment, it is preferable to make a product(μa/D1) of an inverse of the distance D1 and a permeability μa of theauxiliary pole 3 greater than a product (μs/D2) of an inverse of thedistance D2 and a permeability μs of the upper shield, the distance D1meaning a spacing between the main pole and the auxiliary pole,concretely, the opposed side of the main pole 1 to the auxiliary poleand the opposed side of the auxiliary pole to the main pole and thedistance D2 meaning a spacing between the main pole and the uppershield, concretely, between the opposed side of the upper shield film 9to the main pole and the opposed side of the main pole 1 to the uppershield film.

In addition, in this embodiment, the trailing side may be reversed inposition to the leading side.

Fourth Embodiment

FIG. 10 is a schematic sectional view showing a magnetic head accordingto a fourth embodiment of the present invention. The section is cut onthe center of the track of the head in the disk rotating direction. Inthis embodiment, the auxiliary poles 3 a and 3 b are located on thetrailing side and the leading side in a manner to sandwich the main pole1. The coil 2 c is located between the main pole 1 and the auxiliarypole 3 a and the coil 2 d is located between the main pole 1 and theauxiliary pole 3 a. The opposed area of the auxiliary pole 3 a to thefloating surface is made greater than the opposed area of the auxiliarypole 3 b to the floating surface and the magneto-motive force of thecoil 2 c, which corresponds to a product of the number of windings ofeach coil 2 c located on the side of the auxiliary pole 3 a with asmaller area and a current applied to the coil, is made greater than themagneto-motive force of the coil 2 d located on the auxiliary pole 3 bwith a larger area. The resulting coils generate the asymmetricalmagneto-motive forces.

In this embodiment, the magneto-motive force of the coil 2 c located onthe leading side is greater than, that is, asymmetrical to that of thecoil 2 d located on the trailing side. Hence, the film thickness t2 ofthe auxiliary pole 3 a located on the leading side is made thinner thanthe film thickness t1 of the auxiliary pole 3 b located on the trailingside. This allows the distance between the read element 7 and the mainpole 1 (concretely, between the read element 7 and the opposed side ofthe main pole 1 to the read element) to be narrowed accordingly. Theresulting composition offers the read and write composite magnetic headthat is suitable to the high-density recording.

In addition, in this embodiment, the trailing side may be reversed inposition to the leading side.

Fifth Embodiment

This embodiment concerns a magnetic disk storage apparatus which issuitable for high-density recording. The magnetic disk storage apparatusincludes a magnetic head of the invention, the magnetic head having amain pole, at least one auxiliary pole, and coils each composed of athin-film conductor coil that are located in a manner to sandwich themain pole and to make the magneto-motive force of the coil located onone side different from that of the coil located on the other side; amagnetic disk medium composed of a soft under layer and a recordinglayer laminated thereon; a magnetic circuit arranged to be opposed tothe magnetic disk medium rotating on the magnetic head and cause themagnetic field coming from the main pole to enter into the auxiliarypole through the recording layer and the under layer, the magnetic fieldcoming from the main pole being applied into the recording layer bypassing current through the coils for writing a magnetizing signal.

As set forth above, the magnetic head for perpendicular recording usesthe structure of the coils asymmetrically located on both sides of themain pole, which includes the write head having the main pole and one ormore auxiliary poles, the read head provided with the read element, andcoils each composed of a thin-film conductor being located on both sideof the main pole, the magneto-motive force of the coil located on oneside being different from that of the coil located on the other side.This coil structure makes it possible to reduce the magnetic fluxdensity flowing through the under layer and thereby to diminish thenoise generated by the under layer without deteriorating the writingmagnetic field strength generated by the main pole.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1-20. (canceled)
 21. A magnetic disk storage apparatus comprising: amagnetic head having a read head and a write head; the read head havinga lower shield, an upper shield, and a read element formed between thelower shield and upper shield; the write head having a main pole, oneauxiliary pole, and coils located on both sides of the main pole; and amagnetic medium having a soft magnetic underlayer and a magneticrecording layer formed above the soft magnetic underlayer, wherein amagnetic field from the main pole enters into the auxiliary pole throughthe magnetic recording layer and the soft magnetic underlayer, the coilsare arranged so as to magnetize the main pole in accordance with anelectrical current flowing in the coils, and the coils generatedifferent respective magneto-motive forces.
 22. A magnetic disk storageapparatus comprising: a magnetic head having a read head and a writehead; the read head having a lower shield, an upper shield, and a readelement formed between the lower shield and upper shield; the write headhaving a main pole, one auxiliary pole located only on one side of themain pole, and coils located on both sides of the main pole; and amagnetic medium having a soft magnetic underlayer and a magneticrecording layer formed above the soft magnetic underlayer, wherein amagnetic field from the main pole enters into the auxiliary pole throughthe magnetic recording layer and the soft magnetic underlayer, the coilsare arranged so as to magnetize the main pole in accordance with anelectrical current flowing in the coils, and a current flowing in thecoil located on the side of the main pole having no auxiliary pole isgreater than a current flowing in the coil located on the side of themain pole having an auxiliary pole.
 23. A magnetic disk storageapparatus comprising: a magnetic head having a read head and a writehead; the read head having a lower shield, an upper shield, and a readelement formed between the lower shield and upper shield; the write headhaving a main pole, one auxiliary pole, located only on one side of themain pole, and coils located on both sides of the main pole; and amagnetic medium having a soft magnetic underlayer and a magneticrecording layer formed above the soft magnetic underlayer, wherein amagnetic field from the main pole enters into the auxiliary pole throughthe magnetic recording layer and the soft magnetic underlayer, the coilsare arranged to as to magnetize the main pole in accordance with anelectrical current flowing in the coils, and a number of windings of thecoil located on the side of the main pole having no auxiliary pole isgreater than that of the coil located on the side of the main polehaving an auxiliary pole.
 24. A magnetic disk storage apparatusaccording to claim 21, wherein the main pole is formed between the readelement and the auxiliary pole.
 25. A magnetic disk storage apparatusaccording to claim 24, wherein a distance between the main pole and theauxiliary pole is smaller than a distance between the main pole and theupper shield.
 26. A magnetic disk storage apparatus according to claim24, wherein a product (μa/D1) of an inverse of the distance Di and apermeability μa of the auxiliary pole is greater than a product (μs/D2)of an inverse of the distance D2 and a permeability As of the uppershield, wherein D1 is the spacing between the main pole and theauxiliary pole, and wherein D2 is the spacing between the main pole andthe upper shield.
 27. A magnetic disk storage apparatus as claimed inclaim 21, wherein said auxiliary pole is located only on one of saidsides of said main pole so that the magneto-motive force of said coillocated on a side of the main pole having no auxiliary pole is greaterthan that of said coil located on a side of the main pole having saidauxiliary pole.
 28. A magnetic disk storage apparatus as claimed inclaim 21, wherein the ratio of the magneto-motive force of one of saidcoils to that of the other of said coils located on said sides of saidmain pole is 1.5 or more.
 29. A magnetic disk storage apparatus asclaimed in claim 21, wherein the ratio of the magneto-motive force ofone of said coils to that of the other of said coils located on saidsides of said main pole is 2.5 or less.
 30. A magnetic disk storageapparatus as claimed in claim 21, wherein said auxiliary pole is locatedonly on one side of said main pole so that a current flowing in saidcoil located on a side of the main pole having no auxiliary pole isgreater than a current flowing in said coil located on a side of themain pole having said auxiliary pole.
 31. A magnetic disk storageapparatus as claimed in claim 30, wherein a ratio of the applied currentvalue of one of said coils to that of the other of said coils located onsaid sides of said main pole is 1.5 or more.
 32. A magnetic disk storageapparatus as claimed in claim 30, wherein a ratio of applied currentvalue of one of said coils to that of the other of said coils located onsaid sides of said main pole is 2.5 or less.
 33. A magnetic disk storageapparatus as claimed in claim 21, wherein said auxiliary pole is locatedonly on one of said sides of said main pole and the number of windingsof said coil located on a side of the main pole having no auxiliary poleis greater than that of said coil located on a side of the main polehaving said auxiliary pole.
 34. A magnetic disk storage apparatus asclaimed in claim 33, wherein a ratio of the number of windings of one ofsaid coils to that of the other of said coils located on said sides ofsaid main pole is 1.5 or more.
 35. A magnetic disk storage apparatus asclaimed in claim 33, wherein a ratio of the number of windings of one ofsaid coils to that of the other of said coils located on said sides ofsaid main pole is 2.5 or less.
 36. A magnetic disk storage apparatus asclaimed in claim 21, wherein each of the coils is composed of a loopedthin-film conductor.
 37. A magnetic disk storage apparatus as claimed inclaim 21, wherein a distance between said main pole and said auxiliarypole is no greater than twice as long as the thickness of each coillocated between said main pole and said auxiliary pole.
 38. A magneticdisk storage apparatus as claimed in claim 21, wherein the opposed areaof one auxiliary pole to a floating surface of the magnetic head is madesmaller than the opposed area of another auxiliary pole to said floatingsurface, and wherein the magneto-motive force of said coil located onthe side of said auxiliary pole having a smaller area is greater thanthat of said coil located on the side of said another auxiliary polehaving a larger area.
 39. A magnetic disk storage apparatus as claimedin claim 38, wherein the current applied to said coil having saidsmaller area is greater than the current applied to said coil havingsaid larger area.
 40. A magnetic disk storage apparatus as claimed inclaim 38, wherein the number of windings located on said auxiliary polehaving said smaller area is greater than that located on said auxiliarypole having said larger area.
 41. A magnetic disk storage apparatus asclaimed in claim 38, wherein said read head is located on the side ofsaid auxiliary pole having said smaller area.